This application claims the priority of the European Patent Application No. 99 111 582.5 filed on Jun. 15, 1999, the disclosure of which is incorporated herein by reference in its entirety.
The present invention concerns a multipurpose cement dispersing polymer, in particular a modified acrylic polymer.
Concrete from ready mix plants or mixed on job sites, used in civil engineering constructions, e.g. anchorage of big bridges, base plates or side walls and box culverts, in building structures such as heavy reinforced structures, concrete filling pipe structures or other complicated structures, requires to be fully compacted to achieve its desired strength and durability. The existing and conventional method for compaction is by vibration of the freshly placed concrete.
A new production system for in situ-casted concrete is needed to improve significantly the cost situation as well as the health and safety aspects on the construction site.
Additionally, self-compacting concrete leads to a higher productivity, shorter building times and to an improved labor environment.
Increased fluidity (known as xe2x80x9cslumpxe2x80x9d and slump-flow) can be effected by using large dosages of water in the concrete, but it is well known that the resulting cement-based structure. exhibits insufficient compactness and will have poor final compressive strength.
In order to avoid excess amount of water, flowing concrete can be produced by the addition of so called superplasticizers or high range water-reducing admixtures (HRWRs), like sulfonated melamine- or naphthalene-formaldehyde polycondensates or ligninsulfonate based admixtures. All of these well known polymers are not capable of causing the treated cement compositions to retain high flowability over a sustained period of time (known as xe2x80x9cslump lifexe2x80x9d) without imparting a significant delay in the initial set time and considerable retardation of early strengths.
An additional disadvantage is the inconstant and very low flow rate of freshly prepared concrete of containing high quantities (e.g. 500 to 700 kgs/m3) of cement and up to 20% of silica fume and fly ash, which flow rate cannot be improved by the use of conventional HRWRs.
For heavy reinforced fresh precast concrete it is desired that the cementitious mixture has sufficient fluidity to flow through and around the reinforcement steel-structure to fill out the mold and level off at the top of the mold.
In the past ten years, various polymer-additives based on so-called polycarboxylic acid salts, e.g. copolymers of acrylic acid with acrylic esters of polyalkylene glycols have been proposed for imparting high water reduction, high flow and prolonged slump life to concrete, but most of them do not lead to self-compacting concrete without causing a too long retardation of the setting time and the early-strength development.
Enhancing early, i.e. 1 day, compressive strengths, is of high importance in the precast and prestressed concrete industry and chemical accelerators such as tertiary alkanolamines, alkali-and alkaline earthmetal thiocyanates, nitrites and halides are known in the art for this purpose and can be added separately to the fresh concrete.
Since calcium chloride and other inorganic salts can initiate corrosion of reinforcing steel embedded in hardened concrete, tertiary alkanolamines, which show both, accelerating and corrosion inhibiting properties are the most recommendable chemical accelerators.
Unfortunately, tertiary amines are well known to act as powerful catalysts for the cleavage of esters and from this reason can not be premixed with the acrylic ester polymers of the art and stored over longer periods, thus causing strongly reduced shelf life of the blend.
In order to improve the stability of such admixtures a deactivated form of alkanolamines was demanded which is reactivated in an alkaline environment.
With the introduction of a super high flow or self compacting concrete, which contains a multipurpose polymer simultaneously acting 1.) as a HRWR, 2) as set- and strength accelerator and 3) as corrosion inhibitor these problems could be solved, particularly the need for vibration can be significantly reduced.
The object of the present invention is to provide a new category of multi-purpose polymers being capable to serve as a cement dispersing agent and which at the same time are set-accelerating and do have shrinkage reducing- and anticorrosive properties to steel. It was furthermore an objective to provide new cement dispersing, set-accelerating-, shrinkage reducing-, anti-corrosive admixtures for cement or mortar.
Said objectives are achieved by means of the modified acrylic polymers according to the main claim. Preferred embodiments are the object of dependent claims.
Surprisingly, it was found that the modified acrylic polymers according to the present invention do provide all the looked for properties, i.e. they could be employed as admixture for cement or mortar and could serve as a cement dispersing agent and at the same time are set-accelerating and do have shrinkage reducing- and anticorrosive properties to steel.
Said polymers according to the present invention are obtainable by reactingxe2x80x94in presence of a strongly acidic catalystxe2x80x941 mol of a poly(acrylic acid) A-1 or a C1-C5-ester thereof, having both a number average molecular weight of from 500 to 20,000 
with 0.01-0.30 mol of a tertiary alkanolamine or a derivative thereof, represented by formula B-1 
and, optionally with 0-0.80 mol of a monofunctional polyalkyleneglycol-monoalkylether, represented by formula D-1
xe2x80x83HOxe2x80x94(CH2CHROxe2x80x94)xR3xe2x80x83xe2x80x83D-1
and/or optionally with 0-0.60 mol of a xcex1-amino-polyalkyleneglycol-xcfx89-alkylether of formula E-1
H2Nxe2x80x94(CH2CHROxe2x80x94)yR3xe2x80x83xe2x80x83E-1
wherein
each R independently represents a hydrogen atom or a methylgroup;
R1 and R2 independently represent a methyl group a hydroxyethyl(CH2CH2OH) group, an acetoxyethyl(CH2CH2OCOCH3) group, a hydroxy-isopropyl(CH2xe2x80x94CHOHxe2x80x94CH3) group, or an acetoxy-isopropyl(CH2xe2x80x94CHOCOCH3xe2x80x94CH3) group;
R3 is a C1-C4-alkyl rest;
M represents hydrogen, a C1-C5-alkyl rest or an alkali metal ion, an alkaline earth metal ion or an ammonium group or a mixture thereof;
a is an integer of 5 to 270;
x and y independently represent integers from 2-250.
The modified acrylic polymers according to the present invention having an improved cement dispersing, set accelerating, early strength enhancing properties with shrinkage-reducing- and corrosion-inhibiting activity to steel, are preferably composed of at least three constituent units selected from the group given by formulas A, B, D and E: 
wherein
each R independently represents a hydrogen atom or a methyl group;
R1 and R2 independently represent a methyl group, a hydroxyethyl(CH2CH2OH) group, an acetoxyethyl (CH2CH2OCOCH3) group, a hydroxy-isopropyl(CH2xe2x80x94CHOHxe2x80x94CH3) group, or an acetoxy-isopropyl(CH2xe2x80x94CHOCOCH3xe2x80x94CH3) group;
R3 is a C1-C4 alkyl rest,
M represents hydrogen, a C1-C5-alkyl rest or an alkali metal ion, an alkaline earth metal ion or an ammonium group or a mixture thereof;
m, n, p and q are numerical values representing the molarity of the constituent units A, B, D, B being present in the polymer, in a proportion of m:n:p:q=(0.1-0.8):(0.01-0.3):(0-0.8):(0-0.6), such, that m+n+p+q=a and p+qxe2x89xa00;
x and y independently represent integers from 2-250.
The indices m, n, p and q indicate that respective numbers of monomer units are present in the polymer, whereby the monomer units are statistically distributed within the polymer.
The inventively found modified acrylic polymers are preferably obtained upon reacting the components A-1, B-1, D-1 and E-1 in presence of concentrated sulfuric acid as a catalyst and maintained at a temperature of about 140xc2x0 to 180xc2x0 C. for a period of from 2 to 8 hours.
In a preferred embodiment, the polyacrylic acid or its C1-C4 alkyl ester has a number average molecular weight of from 1,000 to 10,000. In another preferred embodiment, the reactant D-1 has a number average molecular weight of from 250 to 10,000, whereas the reactant E-1 has a number average molecular weight of from 250 to 10,000. The integers given for xe2x80x9caxe2x80x9d approximately correspond to the molecular weight range of 500 to 20,000.
A preferred alkanolamine B-1 is a N,N-dialkyl alkanolamine, more preferably N,N-dialkyl alkanolamine is N,N-dimethylmonoethanol amine.
The invention is based on extensive studies of modified acrylic polymers having
1) a poly(oxyalkylene) chain, and
2) a tertiary alkanolamine group,
which both are connected to the backbone of the polymer via ester bonds. In particular, the relationship between the molar ratio of the free carboxylate groups to the polyoxyethylene ester groups in the polymer as well as the length of the polyoxyethylene chain and the performance of the copolymer as a dispersing and waterreducing agent was investigated.
The accelerating and anticorrosive effect of tertiary alkanolamines in aqueous solutions is known for long time. The inventive polymers react in alkaline cementitious compositions and the alkanolamine group is released from the polymer, which is partially adsorbed onto the cement surface. Due, in particular, to their close proximity to the cement surface, the released alkanolamines display a high set-accelerating and shrinkage-reducing effect.
Moreover, it can be supposed that the polymers also are adsorbed onto the reinforcing steel bars within the fresh concrete, where they can act as corrosion inhibitors directly on the surface of said steel.
The preparation of the inventive modified acrylic polymers was carried out according to the synthetic route described in the below reaction scheme:
Reaction Schemexe2x80x94Preferred Synthesis of the Inventive Polymers
1 mol of a polyacrylic acid of MW 2,000-10,000 is reacted at elevated temperature with p moles polyalkyleneglycol-monoalkylether, q moles of an alpha-amino-polyalkyleneglycol-xcfx89-monoalkylether and n moles of a tertiary alkamolamine in presence of an acid catalyst: 
Following to a further aspect of the present invention the inventive polymers are employed for preparing a cement-dispersing, set-accelerating admixture having shrinkage-reducing- and anticorrosive properties to steel. Hence, further to the modified acrylic polymer according to the invention, said admixture preferably contains at least one defoaming or antifoaming agent and or at least one air-controlling agent.
Still a further aspect of the present invention is a mortar, concrete, cement or cementitious binder containing the modified acrylic polymer according to the present invention in an amount of 0.01 to 10% by weight of the binder, said mortar or concrete having a unit content of binder composed of cement or a mixture of cement and latent hydraulic or inert microscopic powder of 150 to 800 kg/m3, preferably of 250 to 650 kg/m3.
In a preferred embodiment, the cement is Portland cement, white cement, high alumina cement, and wherein the latent hydraulic or inert microscopic powder is fly ash, slag, natural pozzolane, silica fume, burnt oil shale, metakaolin or calcium carbonate.
The inventive admixture could be used in liquid form or as a powder form and could be added before, during or after the grinding operation of the cement or the cementitious binder.
A final aspect of the present invention is the use of a modified acrylic polymer according to the present invention as a cement dispersing agent, which is set-accelerating and has shrinkage reducing- and has anticorrosive properties to steel.